Giant-buster

Weapon (any sword), rare (requires attunement)

The giant-buster sword is specifically designed and enchanted to allow Medium humanoids to go toe-to-toe (or, more relevantly, blade-to-blade) with larger foes. Often, Much larger foes. A typical giant-buster sword is an enormous straight blade with a sharply angled tip (scaled for Huge creatures), a long unornamented handle (scaled for Medium creatures, and thus often looking a bit spindly when compared to the blade), and little else.

When fighting with a giant-buster sword, you can use it to make a melee attack against any foe within 15 feet of you. You cannot use it to take attacks as bonus actions. If you score a critical hit on a creature that is Medium or smaller, you knock that target prone.

Creatures of Huge or larger size that can multiattack with a melee weapon take disadvantage on melee multiattacks made against you, because of your ability to block and parry their oversized weapons with your own while maintain a (relatively) minute area for them to strike at. Flung rocks, be they from giants, siege weapons or other sources, are similarly at disadvantage on attacks against you because of your ability to parry with your giant buster.